CONSERVATION PALEOBIOLOGY AND TAPHONOMY: DIFFERENTIAL PRESERVATION AND TIME-AVERAGING OF ECHINOIDS AND MOLLUSKS

Surficial skeletal remains of marine benthos accumulating on modern seafloors are a major source of paleontological data for conservation paleobiologists. A better understanding of how these remains are affected by taphonomic processes/filters, such as time averaging and fragmentation, should allow for more proficient utilization of this archive. To this end, we conducted a comparative live-dead analysis of echinoids and mollusks to assess multiple hypotheses regarding their preservational potential and the resolution of their fossil record. Sediment samples were collected via SCUBA from shallow, marine habitats near Cedar Key (CK) and the Florida Keys (FK). Collections occurred at surface (0-10 cm) and subsurface (30-40 cm) depths within the taphonomically active zone. Following sieving of the samples through 1mm mesh, retained skeletal materials (>1 mm) were dried, sorted by taxa, and classified into live collected, whole dead, and fragments. Samples from CK and FK sites differed in faunal composition but showed similar patterns. By weight, when compared to whole dead specimens, live collected echinoids were proportionally more common than live collected mollusks (FK: 88.9% live echinoids vs 0.5% live mollusks; CK: 25.4% live echinoids vs 3.8% live mollusks). Fragmentation rates were also similar for both sites, with fragments making up 80-89% of all mollusk remains and >99% of all echinoid remains by weight. Subsurface samples showed similar compositional patterns to those observed for surface samples. These results support the hypothesis that echinoid tests disintegrate more rapidly than mollusk shells and thus are less likely to wholly preserve within time-averaged assemblages formed under low-net accumulation rates. Echinoid fragments seem to not follow this pattern, preserving similarly to mollusk fragments. Radiocarbon dating of whole and fragmentary specimens further corroborates these trends, with complete echinoid tests yielding significantly younger radiocarbon ages than echinoid fragments, mollusk fragments, and whole mollusk shells. The results support the notion that geohistorical records provided by echinoids and mollusks may be fundamentally distinct from one another in terms of temporal resolution and completeness of the fossil record.